This invention relates to systems for digitising images. Digitisation is required for example if the image is acquired in analogue form and it is desired to make it amenable to computer analysis or processing.
One such method of acquiring the image is by the use of a scanning camera such as a television camera. That scans an optically formed image in a raster pattern and outputs a varying analogue signal that at each moment represents the optical intensity and/or colour, hereinafter referred to as "display value", of the spot of the image reached by the scan. The analogue signal may then be digitised by being passed to an analogue to digital converter which repeatedly converts the momentary analogue value to the equivalent digital value. The successive digital values then define the intensity and/or colour of each of the different picture elements into which the image may be regarded as being divided.
All the digitised values must be stored if they are to be used by other digital equipment. Hitherto, that has required a store which is both large enough to accept all the digitised data and fast enough to allow values to be loaded at the rate they are produced in response to the scan. If the scan is reasonably fast, as for example with a television camera, that has required a very fast store which for the amount of data involved is very expensive.